The present invention relates to a method and apparatus for drying tobacco, and more particularly to improvements in a method and apparatus for drying tobacco which is conveyed in the form of a continuous stream. Still more particularly, the invention relates to improvements in a method and apparatus for drying tobacco which forms a continuous stream and is caused to advance through a conditioning zone wherein the particles of tobacco are directly contacted by a hot gaseous fluid and the heat content of hot air is regulated in dependency on the moisture content of dried tobacco.
German Offenlegungsschrift No. 1,901,690 discloses a method and apparatus for drying tobacco wherein the temperature of a hot gaseous fluid (normally air) which directly contacts tobacco particles in a conditioning zone is maintained at a value which is regulated with a view to ensure that the moisture content of dried tobacco matches or closely approximates the desired moisture content. This means that the moisture content of tobacco particles which leave the conditioning zone is satisfactory (i.e., it matches the desired or optimum moisture content) but the temperature of dried tobacco fluctuates in dependency on fluctuations of the temperature of gaseous fluid which is utilized to directly contact the particles in the conditioning zone for the purpose of removing moisture therefrom. Such fluctuations of the temperature of dried tobacco particles entail fluctuations in the rate of evaporation of moisture upon completion of the drying operation. In other words, once the dried tobacco is cooled, its moisture content is not uniform owing to different rates of evaporation of moisture during cooling. The deviations of moisture content of cooled tobacco from the desired moisture content are not very pronounced but suffice to reduce the quality of the ultimate products, such as cigarettes, for example, by adversely affecting the so-called filling force of tobacco particles in the wrapper of a rod-shaped smokers' product.